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Dense Wavelength Division Multiplexing (DWDM)

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Outline

 What is fiber optics  Advantages of fiber optics  Bandwidth Demand  Options for increasing the bandwidth  Time Division Multiplexing (TDM)  Wavelength Division Multiplexing (WDM)

 TDM and WDM comparison  WDM History and Evolution  Major elements of an optical fiber link

 Optical Networking – The DWDM  DWDM Components  Optical Amplifiers  Development Trends of Ethernet  Ethernet Transport Methods  Network Management System (NMS)  DWDM Benefits

 DWDM Summary

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What is Fiber Optics ?

Transmission of communication signals in the form of light over thin glass or plastic (Fiber). Pulses of infrared light guided through glass fibers move huge blocks of data over long or short distances Propagation of Light in a Fiber Fiber Structure

n1 n2

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Advantages of Fiber Optics

 Higher data rates

 Low Loss  Longer Distance  Less Weight / Size  Freedom from Interference  Electrical Isolation  Security

This single fiber can carry more communications than the giant copper cable

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Bandwidth Demand

Data 250

Data Traffic overtakes Voice Traffic 200

Voice Traffic ďƒ 13 %

150

Data Traffic ďƒ 300 %

Voice

100

And at the same time number of users also increasing

50

1990

1993

Voice-centric

1996

1999

2002

2005

Data-centric

* Source: Cisco Systems White Paper Commtel Networks Proprietary


Options for Increasing the Bandwidth

More Fibers

Installing new fibers

Same bit rate, more fibers Estimated cost is about Rs. 1,75,000 per km

Faster Electronics (TDM)

Increasing the bit rate Higher bit rate, same fiber Expensive and Complex Electronics

WDM

Increasing the number of wavelengths

Same fiber & bit rate, more wavelengths

* TDM and WDM ď‚Ž Increases the effective capacity of the existing fiber

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Time Division Multiplexing (TDM) Definition : TDM is type of multiplexing, that transmits multiple signals simultaneously over a single transmission path by assinging each stream a different time slot. Bits of Information

Fiber TDM

Mux

Time slot

Synchronous Digital Hierarchy (SDH)  a standard for optical transport of TDM data STM-1

 155 Mb/s

STM-4

 622 Mb/s

STM-16  2.5 Gb/s

STM-64

 10 Gb/s

STM-256  40 Gb/s *

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* Recent Developments


TDM Limitations at Higher Bit Rate

 Expensive and Complex Electronics

 Complex Modulation  SNR Decreases

TDM DS-1 DS-3 STM-1 STM-4 STM-16

Channel 1 . . . Channel N

Single Fiber (One Wavelength)

 Dispersion is very high

* Transmission at 40 Gb/s (STM-256) over single-mode (SM) fiber is 16 times more affected by Dispersion than the transmission at 10 Gb/s (STM-64).

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Wavelength Division Multiplexing (WDM) *

WDM increases the carrying capacity of the physical medium (Fiber) using a completely different method from TDM

Definition : Multiplexing several optical signals having different wavelengths and transmitting simultaneously over a single fiber is known as wavelength division multiplexing. 2.5 Gb/s

Fiber 10 Gb/s

1

TDM Mux 2.5 Gb/s

Fiber 30 Gb/s Fiber 10 Gb/s 2

TDM Mux

2.5 Gb/s

WDM MUX

Fiber 10 Gb/s 3 TDM Mux

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TDM and WDM Comparison TDM

 Time Division Multiplexing (TDM) DS-1 DS-3 STM-1 STM-4 STM-16

 Single wavelength per fiber  Multiple channels per fiber  E/O or O/E/O Conversion  Common signal format

Channel 1 . . . Channel N

Single Fiber (One Wavelength)

 Takes sync and async signals and multiplexes them to a single higher optical bit rate

WDM

 Wavelength Division Multiplexing (WDM) STM-4 STM-16 STM-64 SDH/SONET ATM GE

 Multiple wavelengths per fiber 2, 4, 16, 64 etc.  Multiple channels per fiber  No O/E conversion  Can carry multiple protocols  Takes multiple optical signals and multiplexes them in to a single fiber

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1

2 3 n

Single Fiber (Multiple Wavelengths)


WDM History

64 to 160 channels in 1550nm window

Late 1990’s

Next generation DWDM systems Channel spacing of 0.2 to 0.4 nm 16 to 40 channels in 1550nm window

Mid 1990’s

Early 1990’s

1980’s

DWDM (Dense WDM)

Channel spacing of 0.8 to 1.6 nm 2 to 8 channels in 1550nm window Passive (or) 2nd generation WDM Channel spacing of ~3.2 nm 2 channels WWDM (Wideband WDM) 1310nm and 1550nm

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WDM Evolution

 Faster (Higher speed per channel)

 Thicker (More channels)  160 channels possible today  Longer (Link lengths before regeneration)

Dense WDM

 A few thousand km possible today

 160 channels at 10 Gb/s = 1.6 Tb/s

1

 25 million simultaneous phone calls

2 WDM MUX

3 -

N

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Electromagnetic Spectrum

Ultraviolet

Infrared

Visible

Radio waves Long waves

X-rays Gamma rays 1.3 1.4

850

1310

1.5 1.6

1.7

Fourth Window

1.1 1.2

Third Window

1.0

Second Window

0.8 0.9

First Window

0.7

1550 1625

ď ­m

nm

Available wavelengths for optical transmission

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Fiber Performance

*

The strength of a signal traveling through an optical fiber weakens with distance

ď ś Attenuation Definition : Loss of signal power in a transmission

z=0

z=L Attenuation

ď ś Dispersion Definition : Broadening of the pulses as they travel along the fiber over long distances

z=0

z=L Dispersion

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1625-1675 U-band

1530-1565 C-band 1565-1625 L-band

1460-1530 S-band

10

1360-1460 E-band

1260-1360 O-band

Attenuation (dB/km)

Fiber Attenuation Vs Wavelength

Standard fiber 1.0

O = Original E = Extended S = Short C = Conventional L = Long U = Ultra-long

0.1 1000

1100

1200

1300

1400

1500

1600

1700

Attenuation (Loss) per kilometer (dB/km) 0.40 dB/km at 1310 nm 0.25 dB/km at 1550 nm Commtel Networks Proprietary

Wavelength (nm)


Dispersion Slope for Different Fibers

ITU-T G.652 ITU-T G.655 ITU-T G.653

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Channel (Wavelength) Spacing

DWDM – Dense Wavelength Division Multiplexing (~ 0.8 nm)

Wavelengths

CWDM – Coarse Wavelength Division Multiplexing (~ 20 nm)

Wavelengths

WWDM – Wide Wavelength Division Multiplexing (~ 100 nm)

Wavelengths

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The ITU-T Wavelength Grid

1563.86 nm

1528.77 nm

0.8 nm 191.7 THz

196.1 THz 100 GHz

The ITU draft standard G.692 defines point-to-point WDM systems based

on 100-GHz wavelength spacing with a center wavelength of 1553.52 nm

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Major elements of an optical fiber link

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Optical Networking – The DWDM

1 2 Data

. .. . . .

1 DWDM Mux

OA OADM

n

OA

DWDM Demux

2

. .. . . .

n Optical Path

OA – Optical Amplifier OADM – Optical Add Drop Multiplexer

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Data


DWDM Components – Transponder Converts broadband optical signals to a specific wavelength

OEO From OLTE

1 2

To DWDM Mux

Receive Transponders

OEO

OEO

perform reverse function n

DWDM Laser - Distributed Feedback (DFB)  High performance telecommunication laser

Power

c

 Long-haul links & DWDM systems  Key characteristics  Mostly around 1550 nm  Total power 3 to 50 mw  Spectral width 10 to 100 MHz (0.08 to 0.8 pm)

 Small NA (good coupling into fiber)

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DWDM Components – Multiplexer & Demultiplexer

 DWDM Multiplexer

Wavelengths Converted via Transponders

 DWDM Demultiplexer

1

1

2

2

3

3

. . . . . .

4

DWDM Mux

DWDM Demux Wavelength Multiplexed Signals

Wavelength Multiplexed Signals

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. . . . . .

4

Separated Wavelengths


DWDM Components – Optical Add/Drop Multiplexer (OADM) OADMs allow flexible add/drop of channels

Drop Channel

Add Channel

+

=

OADM

Circulator Based OADM

Three Isolated Ports

In

2

1 3

Drop

FBG

Bragg= 3

3

2

Out

 Port 1  Port 2  Port 2  Port 3  Port 3  Port 1

1

Add

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* FBG = Fiber Bragg Grating


DWDM Components – Optical Amplifier (EDFA)

 EDFA – Erbium Doped Fiber Amplifier Optical Amplification

Loss

OA

 EDFA Construction  Simple device consisting of four parts

Pump Signal

 Erbium doped fiber  An optical pump

Isolator

 A coupler  An Isolator to avoid back propagation noise Input Signal

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Erbium Doped Fiber

Amplified Output Signal


EDFA - Basics  Absorption

 Spontaneous Emission

When a light incidents on the atom the electrons

Light is spontaneously emitted when an electron

in the lower energy state absorbs the energy,

decays from higher energy state to the lower

jumps into higher energy state.

energy state.

Higher Energy States

Lower Energy State

 Stimulated Emission

When a light incidents on the excited state electrons, electrons decays from higher to the lower energy state by emitting the light twice as and identical to the incident light

 Same wavelength, Direction and Phase

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EDFA – Operation

 Dope a fiber with Erbium

 Pump energy into the fiber

 Transmit and amplify the signal

Higher Energy States

980nm Pump

1550nm Amplification

Lower Energy State

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EDFA

Pump Signal into Erbium doped fiber

Erbium Doped Fiber

Input Signal

Coupler

EDFA gain (dB)

30

Amplified Output Signal puls ASE Noise

ď Źpump = 980nm

20

Pin = -25 dBm

10

Length = 16 m

0 -10 1520 1530 1540 1550 1560 1570 wavelength (nm)

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EDFA – Input and Output Spectrum

Signal Spectrum

Amplifier Spectrum with no Input

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Amplified Signal Spectrum (Amplified Signal + ASE)


DWDM with EDFA

2

2

n-1

Demultiplexer

1 Multiplexer

1

EDFA

n-1 n

n

16 Channels Spacing at 100GHz. 0.8nm

ASE C- Band 1530 to 1565

C- Band 1530 to 1565 Commtel Networks Proprietary


EDFA Design Issues

 The main parameters in the design of an EDFA  Fiber glass material  Characteristics of the fiber

 Erbium concentration profile  Erbium fiber length  Pump sources  Passive or active components such as couplers, isolators

 Primary design goals  High gain  High output power  Low noise figure  Flatness of the gain spectrum  Reliability

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EDFA - Applications

 Booster Amplifier EDFA is located with the transmitter and is used to boost the transmitter signal to a high level in order to drive a long fibre

Transmitter

EDFA

Receiver

 In-Line Amplifier In an in-line amplifier configuration, the EDFA is used to amplify the weakening signal for further transmission down the line.

EDFA

Transmitter

Receiver

 Pre Amplifier The pre-amplifier application is similar to In-Line application; however the EDFA is typically located with the receiver to amplify the signal just prior to its reception.

Transmitter

EDFA

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Receiver


Development Trends of Ethernet

A Networking technology that allows multiple network stations (computers, printers, servers, terminals, etc.) to communicate.

 Technology Advantages  Very adaptable  Reliable  Uncomplicated technology  Plug and play solution  Both the service providers and the end users are comfortable with Ethernet  Ethernet has many years of usage and study

* 85 - 90% LANs are Ethernet based

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Triple Play Services

 Customer Needs  Internet Access  LAN to LAN Connectivity (centralized server access)  File transfer

Voice Data Video

Ethernet Pipe

 Video Conferencing  Backup, Disaster recovery and Business continuity  Business telephony

Voice

Telephone Network

Data

IP Network

Voice

Data

Telephone Network

IP Network

Video

Video

Broadcast Network

Voice, Data and Video will converge and share a common IP network

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Broadcast Network


Ethernet Transport Methods

B-ISDN IP ATM SDH/SONET Optical

IP over SDH/SONET IP SDH/SONET Optical

Development of IP Network

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IP over DWDM

IP DWDM


Data Network Systems

Transmission

Ethernet, Fast Ethernet, Gigabit Ethernet

Ethernet

Header

IP Header

TCP Header

Data

Error Correction

ď ś Most networks and subscriber interfaces, adopt IEEE 802.3 standards (Ethernet)

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IP over SDH/SONET SDH/SONET Network

SDH/SONET Multiplexer

Ethernet mapping via VCAT, LCAS or GFP Ethernet, Fast Ethernet, Gigabit Ethernet  TDM Based  Ethernet adaptor interfaces on SDH Mux  Ethernet mapped to SDH payload  Virtual Concatenation (VCAT)  Link Capacity Adjustment Scheme (LCAS – ITU X.86)  Generic Framing Procedure (GFP)  Unequal bandwidth utilization

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IP over DWDM DWDM Network

DWDM Multiplexer Ethernet, Fast Ethernet, Gigabit Ethernet  WDM Based  Map Ethernet directly to a wavelength  1 GbE – 1GBase-SX and 1GBase-LX • DWDM implements up to 120 Km, cascaded EDFAs extends the reach to 1600+ Kms  10 GbE – 10GBase-SR, 10GBase-LR and 10GBase-LX4 • DWDM implements up to 80 Km, cascaded EDFAs extends the reach to 1000+ Kms  Increases the fiber capacity  Unidirectional and Bi-directional wavelengths

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Protocol Transparency

SDH/SONET ATM IP Fast Ethernet Gigabit Ethernet Fibre Channel FDDI ESCON

DWDM Demux

DWDM Mux

ď ś Data rate and format adaptation without reconfiguration

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SDH/SONET ATM IP Fast Ethernet Gigabit Ethernet Fibre Channel FDDI ESCON


Network Management System

Network management is an essential element of communication systems since it is responsible for ensuring the efficient, secure and continuous functioning of any network.  Functions of Network Management NMS

 Configuration Management  Fault Management

sub-network(s)

 Performance Management  Accounting Management  Security Management

DCN

sub-network(s)

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EMS


NMS – Functional Architecture

NMS

Network Management Layer

EMS

EMS

Element Management Layer

Agent

Agent

Agent

NEs

NEs

NEs

NMS : Network Management System EMS : Element Management System NEs : Network Elements – OTM, OADM, OA Etc.

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DWDM - Benefits

 Capacity Increase  Large aggregate transmission capacity

 Upgradability  Customer growth without requiring additional fiber to be laid

 Flexibility  Optical Add/Drop Multiplexing (OADM)  Optical Cross Connect (OXC)

 Scalability  The possibility to add new nodes to the network

 Network Transparency  Independence of data rate, format and protocols

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DWDM - Summary

 DWDM provides enormous amounts of scaleable transmission capacity  DWDM technology gives us the ability to expand fiber network rapidly to meet growing demands of customer  The DWDM systems provide transparency to various bit rates and protocols  Utilizes the existing thin fiber  DWDM improves signal transmission  DWDM allows flexible add/drop of channels (OADMs)  Bi-directional communication using a single fiber can be achieved by the use of two different wavelengths, one for each direction  Transmission over the longest possible distance with smallest number of optical amplifiers  IP over DWDM

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Undersea Cables

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Thank You pnamala@commtelnetworks.com www.commtelnetworks.com

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Technical Presentation on DWDM System  

Technical Presentation

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